In the very near future, a new type of video and television will enter the family living room. What happened to the music industry with the introduction of the Digital Compact Disc is now happening to the video and television industry. New technology has made it possible to compress and broadcast digital images at a speed fast enough to produce a motion picture. Some of the advantages of digital TV include a better image quality and new possibilities to interactively manipulate the images from a chair in the living room. But as always, this new technology presents new problems. As with other digital data, e.g., software, CD-ROMS and music CD's, a digital video sequence can be copied into an exact duplicate of the original, making it impossible to distinguish the copy from the original. Sale of illegally copied video films already are a major problem for the film industry, but until now the inferior quality of the illegal copies made it easy to unveil the fact that they actually are copies, making it difficult for a person to buy an illegal copy unintentionally. With the digital video anybody can be fooled, unless some authentication system is introduced. Another problem can arise in the broadcasting of TV news. A TV channel is not allowed to use what another TV channel has broadcast without a permission. Until now there have been no major problems with TV channels stealing from each other, due to the loss of quality a retransmission implies. Further, TV stations are normally superimposing a small channel logo on the images they broadcast making authentication of the source easy. If the images are digital there will be no loss of quality and it will be very easy to remove the channel logo, and even superimpose another logo instead. Consequently, a better means to provide the authentication is needed.
With the growth of digital networks, a need has appeared for a mechanism capable of protecting the ownership of video or image authors. A classical means to protect image or video material is known as "Digital Signature", where the video/image-data material is slightly modified ("signed") in order to embed a number or image or other information, which can later be retrieved. This embedded number can then be used either to identify the author or the organization who created the material. Two main "signing" techniques are classically used. The simplest one consists of modulating the luminance of random chosen pixels and is particularly suited for gray-scale images as can be found in an article by R. G. van Schyndel, et al. ("Digital watermark," Proceedings of the 1994 1st IEEE International Conference on Image Processing, Vol. 2, pp. 86-90, 1994). More complex techniques can also be found where the image is cut in blocks, with a modulation amplitude and block size which are themselves modulated by local energy. Work by K. Matsui et al., ("Video-Steganography: How to secretly embed a signature in a picture," The Journal of the interactive Multimedia Association Intellectual Property Project, Vol. 1, No. 1, pp. 187-206, January 1994) proposes a block-based method where the dithering rule is modified. In an article by W. Bender et al. ("Techniques for Data Hiding," Proceedings of the SPIE, 2420:40, February 1995), the difference between pixel luminance value is used. Whereas W. Bender et al. propose to duplicate textured regions and then use autocorrelation computation, one often used technique is also the modification DCT coefficients generated by either JPEG (see S. Burgett et al. "A Novel Method for Copyright Labelling Digitized Image Data," IEEE Transactions on Communications, September 1994), or MPEG-2 coders. These two techniques are well adapted for color images and animated color images, respectively.